A study comparing microvolume fluorimetry (MVF) to flow cytometry (FC) for quantitation of CD34+ hematopoietic cells was published in August 1997 (Read et al., J Hematotherapy 1 997;6:29 1-301). This study demonstrated the potential utility of the MVF method as a simpler, more rapid alternative to standard FC methods for product quality control and for clinical decision making about the timing or duration of stem cell apheresis. An extension of this study was carried out this year to validate the use of a new capillary configuration (plastic, with larger volume) and modified analytic software for the MVF CD34+ cell assay on samples of peripheral blood, leukapheresis collections, and bone marrow. Beginning in October 1997, we will evaluate a new MVF assay for rapid quantitation of CD3+ lymphocytes in hematopoietic progenitor cell collections.